Testing apparatus for radio alarm systems



Oct. 28, l, 947. .J. D. HOLLAND ET AL 2,429,524

TESTING APPARATUS FOR RADIO ALARM SYSTEMS Filed Feb. .15 1943 i I RR I r K Radio Alarm I Y 20 Receiver l: C- Resonanf I cmzuit tunedto wavelength of alarm A 1 signal. /v v 20 7 Radio Alarm v Receiver v INVENTORS John 1). Holland ATTORNEY Patented Oct. 28, 1947 APPA ATU R DIO LA SYSTEMS John. Douglas; Holland and Duncan Dove Robinw 59. Lendon WrC. 2, England assignors, by mesne asSig' ments, to International Standard e ic noratiom, New Kerk N- L, r oe ieh. Delawa e Application February 13, 1943, Serial No. 47,5,7ei0 In Great Britain March 21, 1942 1a c i s. (01. 250-20) The present invention relates to automatic alarm arr emen us d. on s psahd in a t ular concernsmeans for testing such arrange: ments.

It is common practicefor shipsto carry ditto-v matic radio alarmreceivers to' enable them to receive S 0 S o he a arm. si nals heut the n ess y f r th co nued p s ce f an er to he en e re es ve d t h wi ee ie a iy s i e eh he-a toma a rm, ut he mey ee eseehat the aerial s ehes n h bin are; in. the r ght Pet ion. T us. i m y-be tha elthe eh t e radi ecei r is pr p r wor ing eideh e a a m an ot be r eei c b au he a ial i net hnheetedt s s n a the ore. t hav a im l te t w i will show not only whether the receiver is prop.- erly adjusted but. also whether the aerial is cohneeted. test w ch has been us the a has been to put a huzzer signal. into the receiver, rom wh h t i e i y possib t0 de rm n w ther ieiver is pera in hut this sicnot i e any hi niat en about the. aer a t o d; of cour e he-pe si le t9 in e lock the aeria eh nee e er sw h. with he tes ar an ment but. this w u dot take care isome fai ure n he aerial s tem itse f, and m re e more t n one aerial switch might. be involved.

The present i v nti n rov d n, equally simple test which, how ver a so takes account of the aerial and gives anindicationas towhether the whole of the receiving system is in proper oh itiqhte r e the al m si nal.-

Aeee ihete th ih i n the e is rov de a r dio lerni s stem compris n a a r l a ciio r e e adapted teb tim d t the aia m a've eheth ineehsi r witch n t e ae ia from the i e eiver to-a a ia e ih ue anee to term. ere with a lfiSQhhh eirhuit tuned to the saidwavele th and m ans to ex te t e ese ant ci i e c u e it tit-generate wa es adap ed to besietectedh -theree iveh- The invention Wihh me e. clearly iind stecd fr he ieucwine deta led. ee erin iehwith er hee t aeeemhahyih d awing Figs. and 2m wh h shew seh matiecireuit eieeiameei tweemhediments,

Reterrihe-teFigh e he. he all; is eohneeted e aswitehS-by in e. Qt .Wh t may heeeh nested th e ieh u... te -e entees a ie 2 e ve n t hewh. at w en sw tch S s n th e s n. the aer a may he e hhe t d through a contact 2 through a change-ever relay RY o a radio ee i er 3,3 The eehhe h t e e RE is: th e eh a e nta 6. ehd the r ay has an operating coil 8 which is energizer; to move h Contact a f, the elay hem h normal :1 i ie wa Irene e htaet and. against. a contact Ijl. Contact U1 is cgn ected to one side a r able ihil e eh e L! th other. side f. wh ch is. is eehhee ed-te eh e th e te ii he eap ei h tween. ae i 6 a earth i in cated in b oken l nes by eneiiii valent eah it C in hereie th ihd etahe .LL nd the value o ihdue ance Ll is adjusted so that it IQITlIlS wit h a ac t a tune ei ehit r sona es t t wave. l heth the na su in t at switch his in the on pe it en the en r i e.- tion of relayhY siiseehheets the ae ial item. n:-

. ver. R and eenh ets it o inductance h t reh e h eeeh h circu t A. s eend .iheuetahe L2 is coupled to inductance LI and is ir cl gied in a eireu om risin I adjus ab e esistanc and. h eet Met. a. bu ze 26., Buz er B n ela RY a e eehnected in hatallel th o g eond e e l an UL ew-naeefiter F and ads 0 to a batter there bein a k y K wh ch e closed to s multan sly Qh rate the buzz r and.

. energiz c 118 e the ela Filter-F r e t bu zer modu ate i a f m be rad ated m the. batter -s hn y ead zw t th emainde of the circuit.

Wh n t e h y K i e es d, the relay R il b c era te sw ch the aerialh i em he ra io e ver RR to the inducta c L and. a th same time the b zz r will he st ed, and l p i di- Cally int pt. the circu t on a ing ther eiet ance R. and theihdhctanee L2. Th s. will excite the tuned cir uit LI, (1 and wa es wil be adiated at t a n th at h a a m. i hel with su fi cient intensity to be picl geii uphy the radio receiver, which should, of course, b tuned to that Wa e ength. The res st nce R is rovi ed tee Jjust the de e of excitat on o the t e circuit- It. il be evident t at i the aer al h u d e isnnec at h switc S. th ond nser Q will be remo from t tuned ehe t h ch will, t e e o e n ra e eseille eh at s me fr uency mu i her he th t 9 wh eh he eeeiver is uned, The fa t. wi i e immed ely e iiehthecause nothing will be detected by the receiver. A similar result will be obtained if there is some fault in the aerial system which afiects the value of the capacity C, in which case if oscillations are generated, the wave length will be altered. Likewise, if the aerial should be properly connected and if the receiver should be defective or wrongly tuned, again no buzzer signals will be obtained.

Thus, when the test is made, a satisfactory indication will only be obtained if the whole of the receiving system including the aerial is in proper condition to receive the alarm signals.-

All that the operator has to do ongoing off duty 1 is to depress key K and if he gets the proper indication in the receiver RR he will be assured that the arrangements are in order.

It will be clear that if desired, the various ele-.

ments shown in the accompanying figurecan be included inside the radio receiver, proper screening means being of course provided, it being understood that the screening means does not'interfere with the radio receiver picking up the sigi nals as explained above.

The switch S has been shown to represent any switch or system of switches which may be con nected with the aerial, and which must be set in a particular way in order that the alarm may. be picked up.

Fig, 1 shows the essentials of the invention,

but certain other details are desirable to make a practical arrangement.

It is found in some cases, that in order to receive the alarm signals, the sensitivity of the receiver has to be so high as to be overloaded by the test signals, so that no very distinctive dif-,

ference is noticeable in the-signals received-if the aerial is connected to the auxiliary circuit,.

able gain type. I

'I'heanode' 2| of the valve V is polarised from a high tension supply at terminal HT+ through a suitable anode impedance Za, the amplified signals being taken from the anode 2| through a blocking condenser Ca, and supplied to the rest of the receiver (not shown) which is connected to the ou terminal 24. A potentiometer comprising resistances R5, R3 and R2 is connected across the high tension supply for the purpose of biasing suitably the cathode 23 of the valve, the usual by-pass condenser C2 being provided. Resistance R2 is connected to resistance R3 through a contact arm 30 of a keying switch KS hereinafter to be described. Input signals are supplied from the aerial A to the control grid .22 of the valve V through the in terminal 25 and through an input transformer T tuned by a condenser C3 to the wave length of the alarm signal.

The circuit of the buzzer B in Figure 2 is sub stantially the same as that of Figure l, but resistance R in Figure 1 is replaced by a condenser C t connected in series with L2 across the buzzer contact 14,.and this contact is shunted by a sparkquenching circuit formed by a condenser 06 and a resistor R5. A condenser C represents the filter F of Figure 1, and the buzzer B and relayRY are operated from the cathode-heating source for the radio receiver. This is a low-tension circuit contacts of the relay RY with a condenser Ci which conveys the waves directly thereto, and to connect the condenser C7 in series with relay contact [0 as shown. The condenser C7 forms with the capacit of the aerial A, i. e., the condenser C, areducing potentiometer by which the buzzer signal "voltage applied to the aerial during the prising a suitable valve V, preferably of the varitest may be reduced to a value such that the radiation of the .test signals from the aerial is negligible, or within some allowable limit.

The condenser C7 has th further advantage of extending the'efiective tuning range of the inductance -L1, because being small compared with (I, it has the effect of reducing the capacity variations of different aerials as seen from the inductance Li- I I "When the, operator goes 'oiT duty and wishes to ascertain whether the aerial and'receiver are in proper order to receive an alarm signal, he depresses the key KS. This connects relay RY and buzzer 13 tel the low-tension supply terminal LT+ through contact 27 andcontact arm 28 so that aerial A is connected to the test apparatus and buzzer B is started, and in addition the closing of switch KS moves contact arm 30 away from contact 31 and against contact 32. The moving of contact arm 30 away from contact 3| removes adjustable resistance, R2 from the circuit and substitutes therefor an adjustable resistance R], thus, changing the bias on cathode 23 of valve V.

The resistance R2 should be adjusted so that C4) so that these waves will operate the receiver, with plenty of margin when R1 has been adjusted in the mannerjdescribed.

The resistances R1, R2 and R3 may be of the order of a few hundredohms, while R5 may be perhaps 10,000 to 100,000 ohms, according to, the potential of the high tension battery, and the bias required for the cathode. .A resistance R4 of ,high value, (perhaps n megohm) is provided to shunt the cathode independently of the key KS, for the purpose of blocking the valve during the operation of thekey, so' that during theperiod whenall the contacts are open, the cathode potential is raised to a high value.

The reason for thisis that while the aerial is being tested it will in general be picking up signals and/or noise which will occupy the dot periods of the SO S signal which the operator uses to test the arrangement. Unless a short interval of no signal is definitely provided, the relays etc. in the part of the receiver not shown may not properly release because of the general noise which may fill up-the dot periods. By blockin the valve ioran instant at the be inningand end of each dot period, during the change-over oi the key, the necessary no signal period is ensured.

It will be understood that various other ways of changing the sensitivity of the receiver :could be used, not necessarily involving a variable gain valve. Moreover, other arrangements of resistances or other biasing means could be employed.

Neither of the resistances R4 or R5 is essential to the invention, though their use is desirable.

The key K can be any suitable switch or relay, but it is preferable that it should not be capable of locking in the operated position so that it cannot be left accidentally in that position.

What is claimedis:

1. A radio alarm system comprising an aerial, a radio receiver arranged to be tuned to an alarm wavelength, a variable inductance discrete from said receiver and adjusted to a value which, when shunted by the aerial-ground capacity will form a circuit resonant to said alarm wavelength, means for switching said aerial from said receiver to said variable inductance to form therewith said resonant circuit tuned to said wavelength, and means to excite said resonant circuit to cause it to generate waves adapted to be detected by said receiver, said receiver including a thermionic valve of the variable gain type and means to change the cathode bias of said valve in response to operation of said switching means to enable said receiver to receive satisfactorily the waves generated by said resonant circuit.

2. A radio system as described in claim 11, wherein said local signal source is energized simultaneously with the operation of said connection means.

3. A radio system as described in claim 11, wherein means is provided in said receiver to adjust the receiver for the proper reception of the signal from the local signal source.

4. A radio system as described in claim 11, wherein means is provided in said receiver to adjust the receiver to correspond with the anticipated magnitude of the signal from said local signal source, and means to operate simultaneously said last named means and said connection means and said local signal source.

5. A radio system as described in claim 11, wherein said receiver includes a thermionic valve of the variable gain type, and means to change the cathode bias of said valve simultaneously with the operation of said connection means whereby the receiver is adjusted in accordance with the anticipated magnitude of the signal from said local signal source.

6. A radio system as described in claim 11, wherein said receiver includes a thermionic valve of the variable gain type, means to change the cathode bias of said valve simultaneously with the operation of said connection means whereby the receiver is adjusted in accordance with the anticipated magnitude of the signal to be received, and means to impose a blocking bias on the cathode during the time that said last-named means is changing the cathode bias.

7. A radio system as described in claim 11, wherein a condenser is provided connecting said tuned circuit to said receiver therebyto provide a direct connection for the test signals.

8. A radio system as described in claim 11, wherein said local signal source is a buzzer and circuit means coupled to said tuned circuit.

9. A radio system as described in claim 11,

wherein-said local signal source is a "buzzer and said means to operate said connection means is the solenoid of a relay connectedln parallel with said buzzer, and filter means to prevent the signals from being radiated through the power supply means.

10. In a radio system, the combination of, an aerial, switch means connected to said aerial andhaving a first position and a'second position, a radio receiver which is tunable to the wave length of an alarm signal and which is connected to said aerial said switch means is in said first position, electrical circuit means which is connected to said aerial when said switch means is in said second position, said electrical circuit means forming with said aerial a tuned circuit resonant to the wave length of said alarm signal, a local source of signals connected to said electrical circuit means to produce oscillations in said tuned circuit at the wave length of said alarm signal, and means to operate said switch means from said first position to said second position whereby said aerial is disconnected from said receiver and is connected to said electrical circuit means with the result that said local signal source cooperates with the resonant circuit formed by said electrical circuit means and said aerial to produce a signal of the wave length of said alarm signal and of suflicient intensity to be picked up by said receiver if said receiver is tuned to the wave length of the alarm signal, whereby the receipt of such signal by said receiver indicates that the entire radio alarm system is in proper operating condition.

11. In a radio system, the combination of, an aerial, connection means connected to said aerial and adapted to connect said aerial alternatively to a first connection or to a second connection, a radio receiver which is tunable to the wave length of an alarm signal and which is connected to said first connection whereby it may be connected by said connection means to said aerial, electrical circuit means connected to said second connection whereby it may be connected to said aerial by said connection means, said electrical circuit means forming with said aerial a tuned circuit resonant to the wave length of said alarm signal, a local source of signals connected to said electrical circuit means to produce oscillations in said tuned circuit at the wave length of said alarm signal, and means to operate said connection means whereby said aerial is disconnected from said first connection and is connected to said second connection with the result that said local source of signals cooperates with the tuned circuit formed by said electrical circuit means and said aerial to produce a test signal of the wave length of said alarm signal and of sufficient intensity to be picked up by said receiver if said receiver is tuned to the wave length of said alarm signal, whereby the receipt of such test signal by said receiver indicates that the entire radio system including the aerial is in proper operating condition.

12. In a radio alarm installation including a radioreceiver adapted to be connected to an aerial and tunable to the wave length of an alarm signal, apparatus for testing the operability of the installation including the aerial comprising, in combination, circuit means which when connected to said aerial forms therewith a tuned circuit resonant to the wave length of said alarm signal, a local source of signals coupled to said tuned circuit and adapted to produce oscillav 7 REFERENCES CITED The following references are of record in the file of this patent:

I UNITED STATES PATEN'I'S Number r Name Date Newbold Nov. 18, 1941 Shea July '7, 1942 Fanning Aug. 22, 1933 

